Earthquake hydrology gets a shake up

Over many centuries, observations from around the world have noticed the effects of earthquakes on the water levels in wells. Earthquake-induced hydrologic responses range from the near-instant seismically triggered soil liquefaction, to longer-term changes in river discharge, spring flows, and well and groundwater levels.

Recent large South Island earthquakes in Fiordland (2009) and Canterbury (2010/11) have repeatedly triggered a response in monitored wells throughout New Zealand, especially those across the Canterbury Plains. Possibly surprising is the great distances over which these responses can occur, with the Fiordland quake affecting groundwater as far afield as Northland.

Thanks to a Marsden Fund grant, a team of researchers led by Dr Simon Cox from GNS Science in Dunedin will investigate the driving mechanisms of groundwater pressures and ground movements, in response to these contrasting major earthquakes.

Dr Cox and his team seek answers to key questions around how hydrologic responses vary with shaking energy, frequency and direction and the extent to which such responses reflect aquifer damage.

Understanding the effects of earthquakes on groundwater systems and the consequences for engineering strength of land is fundamental in a tectonically active country like New Zealand, which also has a heavy reliance on groundwater resources.

These recent quakes provide a unique opportunity to unravel the cause and driving mechanism of earthquake-induced fluid movements in the earth’s shallow crust. The insights gained will be of national and global significance.

Liquefaction and water: Recent earthquakes in New Zealand generated widespread hydrological effects ranging from near-instantaneous co-seismic liquefaction and changes in well water levels, to more sustained (days to weeks) post-seismic changes in spring flow, river discharge and groundwater piezometric levels, to long-term shifts in groundwater level after one year. Photograph: Liquefaction in eastern Christchurch, Alun Davies, Dec 2011